The present invention relates to oral compositions containing an anticalculus agent.
"Oral composition" means a composition for topical applications to the oral cavity to clean and care for the teeth as well as the oral cavity surfaces. Representatives of such compositions are oral hygiene products and dentifrices such as mouthwashes or rinses, toothpaste, dental gels, tooth powder, chewing gum, lozenges, and similar products. In addition to cleaning teeth to remove dental plaque, the function of oral hygiene preparations is to stop the formation of dental calculus, to prevent dental disorders such as caries, periodontitis and gingivitis, and also to eliminate halitosis.
Dental calculus, or tartar as it is sometimes called, is a hard mineralized material which forms on teeth that consists of inorganic and organic components. The inorganic portion is largely calcium and orthophosphate arranged in a crystal lattice called hydroxyapatite (HAP). The organic portion is derived mainly from microorganisms (i.e., bacteria, yeast, etc.) as well as epithelial cells, white blood cells and food debris.
Formation of dental calculus occurs in two steps. In the first step, plaque is deposited on the teeth. "Plaque" consists of inorganic and organic components derived from saliva, food and bacteria which are present in the oral cavity. Most of the plaque consists of dead and living bacteria surrounded by a gel-like matrix derived from the bacteria and saliva. In the second phase, plaque undergoes calcification to form dental calculus. Initially, amorphous deposits of calcium phosphate begin to appear on and within the matrix of the dental plaque. As the aggregates of calcium phosphate become sufficiently closely packed together, they crystallize to form HAP. The amorphous calcium phosphate, although related to hydroxyapatite, differs from it in crystal structure, particle morphology and stoichiometry.
The presence of both the bacteria and the plaque deposits is detrimental to the health of the teeth and gums. If the bacteria and the plaque formation are not checked, they may result in infected gingival tissue, the formation of dental caries and periodontal disease.
A wide variety of chemical and biological agents have been suggested in the art to retard calculus formation or to remove calculus after it is formed. Mechanical removal of this material periodically by the dentist is, of course, a routine dental office procedure.
Inhibition of oral bacteria involved in the formation of plaque by antibiotics or antiseptic agents is one means to retard the formation of calculus; see, for example, P. S. Hull, J. Clinical Periodontology 7, 431-442 (1980). Examples of antiseptic agents include bisbiguanides, such as chlorhexidine and alexidine, and numerous antibacterially active quaternary ammonium compounds, such as cetylpyridinium chloride or the quaternary ammonium compounds described in U.S. Pat. Nos. 3,369,046 and 4,820,507; and quaternary ammonium organosiloxane compounds described in U.S. Pat. No. 4,161,518.
Although the quaternary ammonium compounds are rapidly adsorbed onto the tooth surface, they exhibit only a moderate degree of efficacy as antiplaque agents as they are rapidly released from the tooth surface and thus retained in the oral cavity for only a short period of time. Chlorhexidine has been the most successful antiplaque agent and is retained in the oral cavity by binding to anionic groups mainly on the oral mucosa. The use of chlorhexidine in oral preparations however, suffers from the following disadvantages: (1) a prolonged bitter aftertaste lasting up to several hours; (2) with prolonged use stains are produced on the teeth, tongue, gums, oral mucosa and dental restorations; and (3) local irritation of the oral mucosa and tongue.
Another means to prevent plaque and calculus formation is to coat the teeth with a material to prevent the release of previously applied therapeutic agents or to coat the teeth with a material containing an antimicrobial agent. U.S. Pat. Nos. 4,243,658; 4,428,930; 4,470,964 and 4,485,090 disclose a dentifrice composition containing a water-dispersible, membrane-forming material which, when applied to tooth surfaces, forms a hydrophobic barrier thereon which substantially reduces elution of a previously applied therapeutic agent. A varnish containing an antimicrobial agent, which provides the sustained release of the antimicrobial agent over a period of at least four days was disclosed in U.S. Pat. No. 4,496,322. The use of the therapeutic agent or varnish coating is not entirely satisfactory as their application requires a qualified professional, making their use as part of routine oral hygiene maintenance impractical.
As the formation of calculus requires the crystallization of HAP, agents which effectively interfere with crystalline materials, including HAP, will be effective as anticalculus agents. Inhibition of crystalline HAP formation is therefore usually achieved by compounds which chelate calcium ions, which prevents the calculus from forming and/or breaks down mature calculus by removing calcium. It is known in the prior art that water-soluble hexametaphosphates, tripolyphosphates and pyrophosphates and the like, are effective calcium and magnesium ion threshold agents, sequestrants and/or chelating agents. A threshold agent has the ability to prevent the precipitation of certain scale forming salts (e.g., calcium carbonate) at concentrations that are much lower than the amount needed for sequestration. See, for example, U.S. Pat. No. 3,488,419, which discloses oral compositions containing polyphosphonate, and U.S. Pat. No. 4,215,105, which discloses oral compositions containing phosphonoacetic acid. The effectiveness of polyphosphonates as anticalculus agents has been limited as they are significantly hydrolyzed by salivary enzymes (phosphatases) to orthophosphates, which are ineffective as inhibitors of HAP formation. The amount of enzymatic hydrolysis of the polyphosphate has been reduced by the use of a linear molecularly dehydrated polyphosphate salt combined with fluoride as described in U.S. Pat. No. 4,808,410.
It is the object of the present invention to provide improved anticalculus oral compositions which inhibit the transformation of amorphous calcium phosphate to HAP crystal structure normally associated with calculus.
Another object of this invention is the provision of an improved method for inhibiting the formation of calculus in the oral cavity.